Within various circuit implementations, such as power supplies, there is often the need to detect a current provided at a particular point within a circuit to use as feedback for controlling other parts of the circuit. Various solutions are presently used to sense currents within electronic circuits but each of these suffer from various shortcomings. A first approach, illustrated in FIG. 1, utilizes a resistor 102 connected across the inputs of an operational amplifier 104 to provide a voltage VSENSE that may be used to determine a current 106. A low value resistor 102 may be used in the range of 10 milliohms. The problem with this approach is the high loss provided by the circuit. This may be overcome by reducing the resistor 102 to reduce the loss, however, this also reduces the signal VSENSE that may be detected. The resistor 102 is not integrated and this type of circuit may be used to sense current within direct current (DC) applications.
Referring now to FIG. 2, there is illustrated a further prior art system utilizing a hall effect device 202 connected across the inputs of an operational amplifier 204. The hall effect device 202 generates a voltage across the inputs of the operational amplifier 204 responsive to the current 206 to provide the output signal VSENSE. While this approach has a low loss, the use of the hall effect device 202 causes the circuit to have a higher cost, and the accuracy and noise issues are greater within the hall device as the hall voltage is a small value. This circuit may also be used to detect current in a direct current (DC) system.
Referring now to FIG. 3, there is illustrated the use of a magneto resistive sensor. The magneto resistive sensor consists of a magneto resistive element 302 connected across the inputs of operational amplifier 304 to detect the current 306. The magneto resistive element 302 has the property that the resistance of the element changes with respect to the magnetic field caused by the current 306. This circuit requires the use of special technology which raises the cost of the device. Additionally, accuracy issues arise even though the current may be sensed with very low loss.
Referring now to FIG. 4, an alternative prior art method for detecting current is through the use of a current transformer 402 is illustrated. The current transformer has a primary side 404 with a single loop and a secondary side 406 with multiple loops. A load resistance 408 is in parallel with the secondary side 406 of the transformer 402. The current transformer 402 is used to detect the current 410. The transformer 402 creates an output current equal to Ip/n with Ip being the detected current and n being the turns ratio of the transformer 402. The resistance of the transformer is reflected to the primary side with the ratio 1/n2. A current transformer will only work within alternating current (AC) circuits. While current transformers work well for detecting currents, they are large and have a medium loss level associated therewith. Thus, some method for detecting a current within a power electronic circuit that overcome the shortcomings of these prior art methods would be greatly desirable.
Another method for measuring currents involves the use of a Rogowski coil. The voltage induced in a Rogowski coil is very small and easily disturbed when measured current is less than, for example, 100 Amps. A Rogowski current transducer has a number of advantages over the current transformer illustrated in FIG. 4. For example, it is linear, has no core saturation effects and has wide band width, wide measurement range and a simple structure. This Rogowski coil comprises a toroidal winding placed around a conductor being measured. It consists of a wire wound on a non-magnetic core. The coil is effectively a mutual inductor coupled to the inductor being measured where the output from the winding is an EMF proportional to the rate of change of current.